U.S. patent number 6,787,398 [Application Number 10/309,595] was granted by the patent office on 2004-09-07 for method of fabricating a high frequency signal amplification device.
This patent grant is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Kunihiko Kanazawa, Kazuki Tateoka, Noriyuki Yoshikawa.
United States Patent |
6,787,398 |
Tateoka , et al. |
September 7, 2004 |
Method of fabricating a high frequency signal amplification
device
Abstract
The present invention provides a high-frequency signal
amplification device, in which insufficient isolation is
compensated and which is made smaller, as well as a method for
manufacturing the same. A substrate, in which a plurality of metal
conductors arranged between the plurality of dielectric layers
and/or at a surface of the dielectric multilayer substrate are
exposed at a first region of the surface, and a metal surface that
is arranged at a position lower than the plurality of metal
conductors is exposed from a remaining portion of the first region
not including the region on which the plurality of metal conductors
are arranged, is used as a dielectric multilayer substrate. The
semiconductor element is mounted in the first region such that a
high-frequency signal is input into the semiconductor element via
at least one of the plurality of metal conductors, and an amplified
high-frequency signal is output from the semiconductor element via
at least another one of the plurality of metal conductors.
Inventors: |
Tateoka; Kazuki (Takatsuki,
JP), Yoshikawa; Noriyuki (Ibaraki, JP),
Kanazawa; Kunihiko (Muko, JP) |
Assignee: |
Matsushita Electric Industrial Co.,
Ltd. (Osaka, JP)
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Family
ID: |
18658832 |
Appl.
No.: |
10/309,595 |
Filed: |
December 3, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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864709 |
May 23, 2001 |
6509641 |
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Foreign Application Priority Data
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|
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May 24, 2000 [JP] |
|
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2000-153611 |
|
Current U.S.
Class: |
438/125;
438/622 |
Current CPC
Class: |
H01L
23/66 (20130101); H01L 2924/0102 (20130101); H01L
2224/49175 (20130101); H01L 2924/3011 (20130101); H01L
2224/451 (20130101); H01L 2224/49171 (20130101); H01L
2924/15153 (20130101); H01L 2224/48091 (20130101); H01L
24/48 (20130101); H01L 2924/00014 (20130101); H01L
2924/12042 (20130101); H01L 2924/1517 (20130101); H01L
24/49 (20130101); H01L 2924/3025 (20130101); H01L
2224/48227 (20130101); H01L 2924/30107 (20130101); H01L
2224/48091 (20130101); H01L 2924/00014 (20130101); H01L
2224/49171 (20130101); H01L 2224/48227 (20130101); H01L
2924/00 (20130101); H01L 2224/49175 (20130101); H01L
2224/48227 (20130101); H01L 2924/00 (20130101); H01L
2224/451 (20130101); H01L 2924/00 (20130101); H01L
2924/00014 (20130101); H01L 2224/45099 (20130101); H01L
2924/12042 (20130101); H01L 2924/00 (20130101) |
Current International
Class: |
H01L
23/66 (20060101); H01L 23/58 (20060101); H01L
021/48 () |
Field of
Search: |
;29/825,829,874
;438/620,623,106,121,125,622 ;174/52.1-52.4
;257/678,700,701,702,728,758,759,77-780 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 614 221 |
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Sep 1994 |
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EP |
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6-314754 |
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Nov 1994 |
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JP |
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06-334449 |
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Dec 1994 |
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JP |
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9-246425 |
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Sep 1997 |
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JP |
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09-283700 |
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Oct 1997 |
|
JP |
|
9-321176 |
|
Dec 1997 |
|
JP |
|
2000-068625 |
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Mar 2000 |
|
JP |
|
Primary Examiner: Chambliss; Alonzo
Attorney, Agent or Firm: Merchant & Gould P.C.
Parent Case Text
This application is a divisional application of application Ser.
No. 09/864,709 filed on May 23, 2001, now U.S. Pat. No. 6,509,641.
Claims
What is claimed is:
1. A method for manufacturing a high-frequency signal amplification
device comprising a dielectric multilayer substrate including a
plurality of dielectric layers, and a semiconductor element with
high-frequency signal amplification function mounted on the
dielectric multilayer substrate; the method comprising steps of:
preparing a dielectric multilayer substrate in which a plurality of
metal conductors are formed on a surface of at least one of the
plurality of dielectric layers, such that, in any range within a
first region of a first surface of the dielectric multilayer
substrate, proceeding from the surface of the dielectric multilayer
substrate in a depth direction of the dielectric multilayer
substrate, the plurality of metal conductors and a metal surface
that is arranged at a position lower than the plurality of metal
conductors is reached before reaching a second surface of the
dielectric multilayer substrate; removing, with an agent capable of
acting in a substantially vertical direction and removing
dielectric materials more readily than metals, in the first region
of the dielectric multilayer substrate, dielectric material from at
least one of the plurality of dielectric layers, in a depth
direction from the first surface of the dielectric multilayer
substrate until reaching the metal conductors and the metal
surface, so as to expose the metal conductors and the metal surface
in the first region; and mounting the semiconductor element in the
first region, such that a high-frequency signal is input into the
semiconductor element via at least one of the plurality of metal
conductors, and an amplified high-frequency signal is output from
the semiconductor element via at least another one of the plurality
of metal conductors.
2. The method according to claim 1, wherein the agent is laser
light.
3. The method according to claim 1, further comprising removing
with the agent, in the first region of the dielectric multilayer
substrate dielectric material between the plurality of conductors,
so as to form in the dielectric material grooves separating the
conductors.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to high-frequency signal
amplification devices and to methods for manufacturing the same.
The present invention particularly suitable to devices for
amplifying signals in high-frequency bands (above 800 MHz,
especially 800 MHz to 2 GHz).
2. Description of the Related Art
Semiconductor elements for amplification of high-frequency signals
(high-frequency amplifiers) used in mobile communication, for
example in cell phones, often are mounted on dielectric multilayer
substrates with multilayer interconnections, in order to achieve
smaller size and lighter weight. Also, to achieve smaller size,
recess portions (cavities) are formed on a portion of the surface
of the dielectric multilayer substrates, and semiconductor elements
are mounted in such cavities.
FIG. 14, FIG. 15 (cross-sectional view along the line V--V in FIG.
14), and FIG. 16 (cross-sectional view along the line VI--VI in
FIG. 14) show an example of a conventional high-frequency signal
amplification device, in which a semiconductor element is mounted
in a cavity. This high-frequency signal amplifier uses a dielectric
multilayer substrate 101 with four dielectric layers 111, 112, 113,
and 114. When layering the dielectric layers, the dielectric layers
are provided with a hole, thus forming a cavity 104. Metal
conductors 102, 103 (131, 132 . . . 137 . . . ) formed on the
dielectric layers 112 and 113 are exposed at the cavity 104. In
this high-frequency signal amplification device, a semiconductor
element 105 is die-bonded to the metal conductor 102, and
wire-bonded with metal wires 106 to the metal conductors 131, 132 .
. . 137 . . . , which are formed at a higher position (closer to
the surface) than the metal conductor 102.
However, when the semiconductor element 105 is made smaller, and
thus the spacing between the metal conductors 131, 132 . . . 137 .
. . is made narrower, in order respond for miniaturization, the
problem of so-called insufficient isolation is aggravated. With
insufficient isolation, capacitive coupling between the metal
conductors tends to occur in the high-frequency band, due to the
shrinking distance L' between the metal conductors (see FIG. 15).
Thus, insufficient isolation leads to instability of the operation
of the element, and depending on the operating conditions, may lead
to oscillations.
In order to eliminate insufficient isolation, JP H07-170090A
suggests providing separation grooves between circuits in a
dielectric substrate with a base metal on which a FET carrier is
mounted. As shown in FIG. 17, a separation groove 201 is formed in
a dielectric substrate 204, for example between an output circuit
202 and an interstage circuit 203 between stages of amplification
with a plurality of FETs. When this separation groove is formed,
the dielectric constant of air (which is 1) in the separation
groove is smaller than the dielectric constant of the dielectric
substrate, so that dielectric coupling due to electric fields
between the circuits can be suppressed. The above-noted publication
also discloses a method for forming the separation groove by die
cutting together with an aperture accommodating the FET carrier
before baking the dielectric substrate.
In order to mount the FETs on the carrier and place the carrier on
the dielectric substrate of the device disclosed in JP H07-170090A,
it is necessary to provide the carrier with die bonding regions,
wire bonding pad regions, etc., and to provide the aperture portion
of the substrate with a margin when placing the carrier. For this
reason, this dielectric substrate is less suitable for
miniaturization than the device using a dielectric multilayer
substrate as shown in FIGS. 14 to 16. Also, since for manufacturing
reasons it is necessary to provide a margin (M' in FIG. 17) between
the edge of the circuits and the edge of the separation groove
disclosed in JP H07-170090A, this margin becomes an obstacle to
shortening the distance between the circuits. Considering the
precision of the actual manufacturing steps, it is necessary to
provide a margin M' of about 200 .mu.m. When this margin cannot be
ensured, there is the danger that the width of the conductors is
reduced by the separation groove, so that their impedance changes,
which leads to a degradation of the high-frequency
characteristics.
Consequently, when trying to apply the separation groove disclosed
in JP H07-170090A to a high-frequency signal amplification device
using the dielectric multilayer substrate shown in FIGS. 14 to 16,
it is necessary to ensure a sufficient margin M', so that the
spacing between the metal conductors becomes large, which runs
counter to attempts to make the device smaller.
SUMMARY OF THE INVENTION
Thus, with conventional high-frequency signal amplification
devices, it is difficult to make the device smaller and at the same
time ensure isolation. Therefore, it is an object of the present
invention to provide a high-frequency signal amplification device,
in which insufficient isolation is compensated and which is made
smaller, as well as a method for manufacturing the same.
In order to achieve this object, a high-frequency signal
amplification device in accordance with the present invention
includes: a dielectric multilayer substrate including a plurality
of dielectric layers; a semiconductor element with high-frequency
signal amplification function mounted on the dielectric multilayer
substrate; a plurality of metal conductors arranged between the
plurality of dielectric layers and/or at a surface of the
dielectric multilayer substrate; and a metal surface that is
arranged at a position lower than the plurality of metal
conductors; wherein the metal conductors are exposed at a portion
of a first region of the surface of the dielectric multilayer
substrate, and the metal surface is exposed from a remaining
portion of the first region not including the region on which the
plurality of metal conductors are arranged; wherein the
semiconductor element is mounted on the first region; and wherein a
high-frequency signal is input into the semiconductor element via
at least one of the plurality of metal conductors, and an amplified
high-frequency signal is output from the semiconductor element via
at least another one of the plurality of metal conductors.
With this high-frequency signal amplification device of the present
invention, dielectric material is removed from a first region
arranged for mounting the semiconductor element, which does not
include the region on which the plurality of metal conductors are
arranged, so that the device can be made smaller and at the same
time, insufficient isolation can be compensated.
In order to achieve the above-mentioned object, a method for
manufacturing a high-frequency signal amplification device
comprising a dielectric multilayer substrate including a plurality
of dielectric layers, and a semiconductor element with
high-frequency signal amplification function mounted on the
dielectric multilayer substrate, includes the steps of: preparing a
dielectric multilayer substrate in which a plurality of metal
conductors are formed on a surface of at least one of the plurality
of dielectric layers, such that, in any range within a first region
of a first surface of the dielectric multilayer substrate,
proceeding from the surface of the dielectric multilayer substrate
in a depth direction of the dielectric multilayer substrate, the
plurality of metal conductors or a metal surface that is arranged
at a position lower than the plurality of metal conductors is
reached before reaching a second surface of the dielectric
multilayer substrate; removing, with an agent capable of acting in
a direction substantially vertical to the surface of the dielectric
multilayer substrate and removing dielectric materials more readily
than metals, in the first region of the dielectric multilayer
substrate, a dielectric layer in a depth direction from the first
surface of the dielectric multilayer substrate until reaching the
metal conductors or the metal surface, and exposing the metal
conductors and the metal surface in the first region; and mounting
the semiconductor element in the first region, such that a
high-frequency signal is input into the semiconductor element via
at least one of the plurality of metal conductors, and an amplified
high-frequency signal is output from the semiconductor element via
at least another one of the plurality of metal conductors.
According to this method for manufacturing a high-frequency signal
amplification device in accordance with the present invention,
dielectric material is selectively removed with laser light, so
that there is no need to provide a margin for manufacturing
reasons, as when forming separation grooves. With this
manufacturing method, a high-frequency signal amplification device
can be provided in which dielectric layers, not including the
region where the metal conductors are formed, are selectively
removed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a dielectric multilayer substrate used in
a high-frequency signal amplification device of the present
invention.
FIG. 2 is a cross-sectional view along the line I--I in FIG. 1.
FIG. 3 is a plan view of a high-frequency signal amplification
device according to the present invention.
FIG. 4 is a cross-sectional view along the line II--II in FIG.
3.
FIG. 5 is a plan view of a signal amplification circuit used in a
high-frequency signal amplification device of the present
invention.
FIG. 6 illustrates the high-frequency coupling in the circuit of
FIG. 5.
FIG. 7 is a graph illustrating the difference in signal leakage for
a high-frequency signal amplification device in accordance with the
present embodiment and a conventional high-frequency signal
amplification device.
FIGS. 8A to 8C illustrate a method for manufacturing a
high-frequency signal amplification device in accordance with the
present invention.
FIG. 9 is a plan view of another dielectric multilayer substrate
used in a high-frequency signal amplification device of the present
invention.
FIG. 10 is a cross-sectional view along the line III--III in FIG.
9.
FIG. 11 is a cross-sectional view along the line IV--IV in FIG.
9.
FIG. 12 is a cross-sectional view illustrating another
high-frequency signal amplification device in accordance with the
present invention.
FIG. 13 is a cross-sectional view illustrating yet another
high-frequency signal amplification device in accordance with the
present invention.
FIG. 14 is a plan view illustrating a conventional high-frequency
signal amplification device.
FIG. 15 is a cross-sectional view along the line V--V in FIG.
14.
FIG. 16 is a cross-sectional view along the line VI--VI in FIG.
14.
FIG. 17 is a cross-sectional view illustrating a separation groove
used for a conventional high-frequency signal amplification
device.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following is a description of the preferred embodiments of the
present invention.
In the high-frequency signal amplification device of the present
invention, it is preferable that the spacing between the metal
conductors for input or output of a high-frequency signal is at
least 10 .mu.m and at most 300 .mu.m. This spacing is suitable to
make the device smaller while ensuring isolation.
In the high-frequency signal amplification device of the present
invention, it is preferable that the semiconductor element is
bonded to the metal surface arranged at a lower position than the
plurality of metal conductors, and that the semiconductor element
is electrically connected to the plurality of metal conductors by
metal wires. The semiconductor element can be bonded face-down to
the plurality of metal conductors.
In the high-frequency signal amplification device of the present
invention, it is preferable that the semiconductor element is
mounted such that it does not protrude upward beyond the surface of
the dielectric multilayer substrate, because this is advantageous
in making the device smaller.
In the high-frequency signal amplification device of the present
invention, it is preferable that the metal surface arranged at a
lower position than the plurality of metal conductors is the
surface of a metal conductor that is arranged on the surface of one
of the plurality of dielectric layers, and that this metal
conductor is disposed over a region that extends at least 50 .mu.m
beyond the edge of the first region. Thus, even if a discrepancy
occurs during the layering of the layered product, it is possible
to manufacture the device in a reliable manner with the
manufacturing method described below.
Moreover, in this high-frequency signal amplification device, the
semiconductor element can be sealed by a resin, in order to protect
the semiconductor element.
The following is a more specific description of the present
invention, with reference to the accompanying drawings.
First Embodiment
FIG. 1 is a plan view of a dielectric multilayer substrate used for
a high-frequency signal amplification device of this embodiment.
FIG. 2 is a cross-sectional view taken along the line I--I in FIG.
1. This dielectric multilayer substrate 1 includes four dielectric
layers (first dielectric layer 11, second dielectric layer 12,
third dielectric layer 13, and fourth dielectric layer 14, layered
in that order from top to bottom in FIG. 2). Metal conductors 3
(31, 32 . . . 37 . . . ) are formed on the surface of the second
dielectric layer 12, and a metal conductor 2 is formed on the
surface of the third dielectric layer 13. Moreover, a through hole
has been machined into the first dielectric layer 11 and the second
dielectric layer 12, so that a recess (cavity) 4 is formed at the
surface of the dielectric multilayer substrate 1.
The outer edge of the cavity 4 is formed like a rectangular frame,
when viewing the dielectric multilayer substrate 1 from above. The
region inside this rectangular frame serves as the mounting region
for a semiconductor element. When viewing the surface provided with
the cavity in the perpendicular direction, only the plurality of
metal conductors 3 (31, 32 . . . 37) and the metal conductor 2 that
is exposed between these metal conductors can be seen in the
mounting region. Thus, the dielectric multilayer substrate 1 is
characterized in that, when viewed from above, substantially only
metal surfaces can be seen in the cavity 4. In other words, in the
cavity 4, the surfaces of the dielectric layers facing the aperture
side are all covered with metal.
In the cavity 4, the metal conductors are arranged between a
plurality of layers (in this example, between two layers). Thus,
the cavity 4 is provided with a step. The edges of the metal
conductors 31, 32 . . . 37 substantially matches with the edge of
the second dielectric layer 12 supporting the conductors.
FIGS. 3 and 4 (cross-sectional view along the line II--II in FIG.
3) show a high-frequency amplification device, in which a
semiconductor element having the function to amplify high-frequency
signals is mounted on a dielectric multilayer substrate. Taking the
lower metal conductor 2 as the die attach surface, the
semiconductor element 5 attached by die-bonding. Furthermore, the
semiconductor element 5 is connected by metal wires 6 to the upper
metal conductors 31, 32 . . . 37 (wire bonding). Thus, utilizing
the multilayer structure of the dielectric multilayer substrate,
circuits are connected to the semiconductor element, and an
amplification circuit for the amplification of high-frequency
signals is accomplished. This circuit includes various receiving
elements (not shown in the drawings). The connection between the
dielectric layers can be performed using via holes. In this
embodiment, utilizing the step in the cavity, the semiconductor
element is mounted at a position that is lower than the metal
conductors for wire bonding, which shortens the length of the metal
wires 6. The shorter the length of the metal wires 6 is, the
smaller is their inductive component.
FIG. 5 is an example of a high-frequency signal amplification
circuit. In this circuit, high-frequency signals that have been
input from an input terminal 51 are amplified with two field-effect
transistors (FETs) 54 and 56, and are output from the output
terminal 59. The FETs are connected to input and/or output matching
circuits 52, 55 and 58, and are further connected to the gate bias
circuits 61 and 63, and to the drain bias circuits 62 and 64.
In such an amplification circuit for high-frequency signals, it is
important to ensure sufficient isolation between the terminals in
order to achieve a stable operation. In the conventional device
shown in the FIGS. 14 to 16, there is a dielectric material with a
high dielectric constant between the metal conductors connecting
the terminals, so that capacitive coupling 60 tends to occur
between the terminals, for example between the input terminal 53 of
the FET 54 serving as the first-stage amplification element and the
output terminal 57 of the FET 56 serving as the second-stage
amplification element, as shown in FIG. 6. When such high-frequency
coupling occurs, the level of signal leakage from the output side
to the input side rises.
However, as shown by this embodiment, when the metal conductors
have to be placed closer to one another near the semiconductor
element in order to connect the semiconductor element, the electric
field concentration between the metal conductors can be diminished
and the insufficient isolation between the terminals can be
compensated, if the dielectric layer between the metal conductors
is eliminated. Moreover, in this embodiment, the dielectric layer
between the metal conductors is eliminated except for the region
that is utilized to support the metal conductor. Consequently, the
electric field concentrations due to the dielectric layer between
the metal conductors are diminished considerably, and the leakage
of signals from the output side to the input side can be suppressed
effectively.
FIG. 7 illustrates the influence of the isolation between the
conductors (metal conductors 31 and 32 in FIG. 2) in comparison for
a high-frequency signal amplification device in accordance with the
present embodiment (with removed dielectric layer) and a
conventional high-frequency signal amplification device (with
remaining dielectric layer; see FIGS. 14 to 16). In particular in
high-frequency bands of ca. 800 MHz and above, the level of signal
leakage can be improved by 10 dB and more with the present
embodiment. In this comparison, the spacing between the conductors
was set to 200 .mu.m.
It is preferable that the spacing between the metal conductors (L
in FIG. 2) is at least 10 .mu.m and at most 300 .mu.m. When the
spacing is too small, the electric field concentration may not be
diminished sufficiently, and when it is too large, it is
inconvenient when making the device smaller, so that this spacing
is more preferably set to at least 50 .mu.m, and even more
preferably to not more 150 .mu.m.
The following is an explanation of a method for manufacturing this
high-frequency signal amplification device.
First, a dielectric multilayer substrate as shown in FIG. 8A is
prepared. Such a dielectric multilayer substrate can be prepared by
any of the conventionally known methods. More specifically, it can
be prepared by taking dielectric sheets with metal conductors
printed in a predetermined arrangement on the surface, and
laminating the dielectric sheets together.
Then, laser light is irradiated on predetermined regions of the
surface of the dielectric multilayer substrate (see FIG. 8B). The
laser light can be irradiated from a substantially direction
perpendicular to the surface of the multilayer substrate in a
scanning motion on a first region of the multilayer substrate. When
irradiating with the laser light, dielectric material absorbing the
energy of the laser light is eliminated, so that dielectric
material can be shaved off the surface of the multilayer substrate.
Also, since the metal does not absorb as much laser light energy as
the dielectric material, it is possible to halt the shaving of
material when reaching the metal surface. Thus, it is possible to
form a recess in the surface of the multilayer substrate, utilizing
the metal surface as a surface for regulating the depth of the
shaving with the laser light. As a result, a dielectric multilayer
substrate having a recess (cavity) 4 as shown in FIGS. 1 and 2 can
be obtained (see FIG. 8C).
There is no particular limitation with regard to the laser light
used for forming the recess as described above, and it is possible
to use a YAG laser, for example. Also, for the dielectric material
and the metal material for forming the metal conductors, it is
possible to use conventional materials, without any particular
restriction. Typical dielectric materials include epoxy resins, for
example. Examples for suitable metal materials include copper. The
irradiation power of the laser light should be high enough to
eliminate the dielectric material and low enough not to eliminate
the metal material during the scanning.
If the cavity is formed by irradiating laser light in this manner,
the edge of the metal conductors can be matched with the edge of
the dielectric layer below these metal conductors. Thus, the other
metal conductor arranged below is exposed between the metal
conductors, and when viewing the region forming the cavity (i.e.
the laser light irradiation region) from above, only metal surfaces
can be seen. It is not possible to achieve such a high precision by
other machining processes, such as die cutting.
Another advantage of machining with laser light is that it is
possible to form the grooves separating the metal conductors even
when the spacing between the metal conductors is small. With
conventional methods, such as the die cutting of unbaked dielectric
sheets, it is difficult to form grooves with a width of less than
100 .mu.m. However, since with laser light it is possible to
adequately follow the precision of the printed metal conductors, it
is possible to form grooves with a width of 30 .mu.m or even
smaller.
Then, a semiconductor element is mounted in the cavity of the
dielectric multilayer substrate, that is, in the semiconductor
element mounting region formed by irradiating the laser light. This
mounting can be carried out by die bonding the semiconductor
element to the exposed metal surface, for example, and then wire
bonding it. Of course, the mounting of the semiconductor element
can also be carried out by face-down methods, such as
flip-chip-bonding, as will be described below, and there is no
limitation to the embodiment shown in the drawings.
As described above, the lower metal conductor 2 functions as a stop
surface for the laser light, but it can be utilized also as a die
chip face for the semiconductor element. Moreover, during
operation, it also functions as a surface shielding the mounting
region from the surrounding noise.
As shown in FIG. 4, in the high-frequency signal amplification
device of the present embodiment, the semiconductor element 5 as
well as the metal wires 6 used for wire bonding are arranged so as
not to protrude upward beyond the surface of the dielectric
multilayer substrate. Such an arrangement is preferable with regard
to making the device smaller, and it is also possible to use the
surface of the multilayer substrate in the cavity 4 as the mounting
surface of the device. Alternatively, it is also possible to take
the surface on the other side as a mounting surface and to mount
another component on the surface of the multilayer substrate in the
cavity 4.
As shown in FIG. 2, in this embodiment, the metal conductor 2 is
formed on a region that extends for the length M beyond the edge of
the cavity 4 (i.e. the first region on which the laser light is
irradiated). This provides a margin taking into account possible
discrepancies in the layering direction when layering the
dielectric layers (layering variations). More specifically, it is
preferable that this margin M is at least 50 .mu.m and at most 200
.mu.m. When the margin is too small, there is the danger that the
shaving with the laser light reaches the lower dielectric layers
when large layering variations occur. When the margin is too large,
it is not suitable for making the device small.
The cavity 4 can be sealed with a resin. As a resin, materials are
suitable that have a lower dielectric constant than the dielectric
material used for the dielectric layers (which often has a
dielectric constant of 4 or greater). Thus, to be specific, it is
preferable that the dielectric constant of the resin is 1 to 3. A
suitable example of resins with such a dielectric constant are
silicon-based resins.
In this embodiment, metal surfaces of two different heights were
provided, but is also possible to form metal surfaces of three or
more different heights, and to form three or more levels in the
cavity. Furthermore, using this cavity, it is also possible to add
other features, such as wiring between the layers.
Second Embodiment
FIG. 9 is a plan view of a dielectric multilayer substrate used for
a high-frequency signal amplification device of this embodiment.
FIG. 10 is a cross-sectional view along the line III--III in FIG.
9. FIG. 11 is a cross-sectional view along the line IV--IV in FIG.
9. Except for the fact that a metal conductor is provided on the
surface of the second dielectric layer 12, the configuration of the
dielectric multilayer substrate 10 is similar to that of the
multilayer substrate 1 explained in the first embodiment. Also in
this dielectric multilayer substrate 10, dielectric material has
been removed from between the metal conductors 3 (31, 32 . . . 37)
to suppress electric field concentrations between the
conductors.
As in the first embodiment, a metal surface (of the metal conductor
2) at an even lower position is exposed between the metal
conductors 3. Also, the metal conductor 2 is exposed between the
metal conductors 3 and 7. Thus, the metal surface (of the metal
conductor 2) formed at a lower position than the conductors 3 and 7
is exposed from the entire mounting region except at the regions
where the metal conductors 3 and 7 are formed.
In this dielectric layer substrate 10, it is preferable that the
spacing W between the metal conductors 3 and 7 is at least 30 .mu.m
and at most 300 .mu.m. When the spacing W is too small, shorts may
occur, and when the spacing W is too large, it is not suitable to
make the device smaller.
Third Embodiment
FIG. 12 is a cross-sectional view of a high-frequency signal
amplification device in accordance with the third embodiment. In
this embodiment, the high-frequency signal amplification device
differs from the previous embodiments in that the semiconductor
element 5 is flip-chip-bonded to the dielectric multilayer
substrate 20 with solder bumps 8. A detailed explanation of the
multilayer substrate has been omitted, as it has basically the same
structure as the multilayer substrates in the previous embodiments.
Also here, dielectric material has been removed between the metal
conductors 31, 32 . . . 34, to suppress electric field
concentrations between the conductors. Also in this embodiment, the
semiconductor element is arranged such that it does not protrude
beyond from the surface of the multilayer substrate, in order to
make the device smaller.
Thus, the present invention also can be applied to arrangements in
which the semiconductor element is mounted face-down.
In the foregoing embodiments, the dielectric multilayer substrate
was made of four dielectric layers, but there is no limitation to
this, and it is also possible to make the dielectric multilayer
substrate of three or less or of five or more substrates. FIG. 13
shows an example of a high-frequency signal amplification device as
in FIG. 12, using a multilayer substrate with three dielectric
layers.
Moreover, in the manufacturing method explained above, it is also
possible to form metal conductors on the surface on the rear side
of the dielectric layers, seen from the direction of the laser
light irradiation.
As described in detail in the foregoing, the present invention
provides a high-frequency signal amplification device, with which
insufficient isolation is compensated and a smaller device is
achieved.
The invention may be embodied in other specific forms without
departing from the spirit or essential characteristics thereof. The
embodiments disclosed in this application are to be considered in
all respects as illustrative and not restrictive, the scope of the
invention being indicated by the appended claims rather than by the
foregoing description. All changes that come within the meaning and
range of equivalency of the claims are intended to be embraced
therein.
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